Why do Tech BC's have the butt dump on the inside, not the outside?

[scubafanatic]

What, no cave divers here? The reason for the dump valve being on the inside is to avoid having it face up where debris and percolation from a cave or wreck ceiling can lodge in the valve and prevent it from closing.

...you know how it goes.....after one too many 'which is the best way to O2-clean my cave snorkel threads' they've long since moved on to 'thedecostop'......

 

[scubafanatic]

Giving the picture post another shot here.

...now THAT'S the scariest thing I've seen since "JAWS" !!!!

 

[scubafanatic]

...now about this long-feared, air-trapping, TACO OF DEATH !!! ...that's diver's got bigger problems....like why is he diving a horseshoe shaped wing and not a donut shaped wing ? ...that's one no-brainer way help distribute/vent gas. Also, gas in the wing only expands on ascent, when the diver is in a heads-up position anyway, in which case the shoulder-dump or inflator hose elevated above one's head will take care of the excess gas.

 

[cool_hardware52]

...now about this long-feared, air-trapping, TACO OF DEATH !!! ...that's diver's got bigger problems....like why is he diving a horseshoe shaped wing and not a donut shaped wing ? ...that's one no-brainer way help distribute/vent gas.

Please explain how a donut wing, with the lower arc of the wing UNDER the cylinders, i.e. between the tanks and the diver's rear end, helps to "distribute/ vent gas?

Also, gas in the wing only expands on ascent, when the diver is in a heads-up position anyway, in which case the shoulder-dump or inflator hose elevated above one's head will take care of the excess gas.

Some of us prefer to ascend in horizontal trim, but just for fun let's examine your thesis. You are correct that most venting occurs during ascents. If it is your SOP to ascend in a heads up attitude how exactly do you benefit form a donut wing?

Do you have some means of suspending the laws of physics and "willing" the gas in your wing to move to the lowest point? (the lower arc, i.e. the part trapped under your cylinder)

Tobin

 

[willembad]

Maybe you should put the tec wings (DR Travel Wing ) away and get some of these...

Willem

 

[Web Monkey]

But see that's the thing, the air trapping is not made up, or I would not be asking the question. There's even a picture of it. (One that I did not post.)

Why not just put the dump in back where there would be no air-trapping?

It's not like someone filled a zip-lock bag with air and hid it in your BC. Why not just tilt slightly in an appropriate direction and vent the wing like the rest of the world?

No matter where the valve is, the wing will "trap" air somewhere, until you make the exahust valve the high point.

And you also have to remember that this is just the butt dump. If you manage to tilt head-up by even a couple of degrees, the exhaust valve on the inflater will work just fine.

Terry

 

[beanojones]

What, no cave divers here? The reason for the dump valve being on the inside is to avoid having it face up where debris and percolation from a cave or wreck ceiling can lodge in the valve and prevent it from closing.

That explanation got put out there earlier. But if it is there to protect the dump, then it is not in the highest position, and traps air. Or alternatively as some said, it is in the highest position because it wraps around the tank, in which case it is not protected.


The fact that most of these explanations contradict themselves is what confuses me. (along with the fact that Dive Rite made a pretty big change at least ten years into making a product, with no explanation of why, and denying that the previous version even existed. It's kind of like the Transpac suddenly turning into a continuous webbing harness, with no acknowledgment that it was ever different.)

 

[beanojones]

IMO Dive Rite "fixed" a problem when they moved the dump to the front (facing diver). With the rear (facing cylinder) dump you pulled towards your body (unless you have 2 elbows)and essentially lowered the valve. It was no longer the high point when the diver is in a horizontal position.

This was said before, and I just don't get what you mean here. I don't see how pulling the dump lowers it, and I don't get why it takes any contortion to reach it mounted either way.


Can you explain that?

 

[beanojones]

It's not like someone filled a zip-lock bag with air and hid it in your BC. Why not just tilt slightly in an appropriate direction and vent the wing like the rest of the world?

(Actually, the vast majority of the world mounts the butt dumps in back. It' only the 'tech' BCs that mount it in front. Hence, this thread, wherein I ask why 'tech' BCD's do it differently than the rest of the world.)

If you look at the picture I circled the trapped air in, the diver would have to roll pretty far over on his side to vent it using the front mounted dump. It is kind of like a ziploc bag of air in there, with the added problem that a front mounted dump has too little fabric to allow it to escape since it cannot be pulled to the highest point. A rear mounted dump can be pulled to the highest point.

 

[Splitlip]

This was said before, and I just don't get what you mean here. I don't see how pulling the dump lowers it, and I don't get why it takes any contortion to reach it mounted either way.


Can you explain that?

Not just a matter of reaching it, but using it effectively.

If you look at the pic of the Red Rec Wing above, clearly it is a reach to get to the string. Once you get the string, the flap in the OPV is pulled away from the wing to exhaust. It would take some kind of monkey arms to pull or push the string in the picture away across the cylinder.
The other option in this case is to get the string an pull towards you or sideways. When you do that the dump is no longer in the high part of the bubble.

Some of the older DR wings even had the dump facing away from the diver but the string and ball were threaded around the wing to face the diver. This to me made no sense unless the diver was pointed head down.

With a diver facing dump, the string is easily grasped and can be pulled to the rear which keeps the valve up high.